The assignee of the present patent application and invention is also the owner of a Horton et al patent application for a Polarity Switch for Satellite Television Receiver having a Ser. No. 695,458 and a filing date of Jan. 18, 1985. In that application, an invention is disclosed which interconnects between the horizontal polarity antenna feed and vertical polarity antenna feed of a dual feed antenna system and a television receiver as is typically used in a satellite television receiver system for receiving, decoding and displaying television signals broadcast from satellites. In the polarity switch disclosed in that application, the pulse width modulated receiver signal generated by the receiver to select between the two antenna feeds is decoded and used to switch a pin diode switch so that the selected antenna feed is transmitted to the receiver. Using the polarity switch of that invention, a plurality of receivers throughout the home and each individual receiver can select and display any channel of either the vertical polarity station group or the horizontal polarity station group. The polarity switch of that invention is a good and valuable invention and has provided a unique solution to adapt the dual feed antenna system to existing receivers.
The inventors herein have succeeded in designing an improved polarity switch which also utilizes a pin diode switch circuit in switching the RF signal path between the receiver and each of the vertical polarity and horizontal polarity antenna inputs. However, this improved polarity switch provides additional advantages and features which are not found in the polarity switch previously disclosed and claimed. For example, a single comparator and its bias circuitry is used to detect the incoming receiver signal and produce a logical 0 or 1 output instead of the two stage detection and comparator design in the prior invention. In the pin diode switch portion of this new circuit, two diodes are used in each switching leg between the antenna input and the receiver input to increase isolation and reliability. Additionally, the unused RF antenna signal is shunted to ground through another switched diode in each leg to further enhance the separation and minimize potential for interference between the antenna inputs. Still another feature is an improved DC power path between the receiver input and each of the antenna inputs to provide DC power to both antenna electronic components, with each DC power path having a steering diode to increase isolation and prevent stray DC signals from interfering with receiver operation. Still another added feature of the present design of the improved polarity switch is that the four switching diodes between the antenna inputs and the receiver input are forward biased with a quiescent voltage to increase circuit reliability and provide back biasing voltages to aid in turning off diodes as they are switched from one mode to another.
In an alternate embodiment, the same comparator circuit is used to detect the receiver signal input, but a pair of relays are substituted for the pin diode switch and its associated driver ciruitry which provides some advantages for some installations over the pin diode switch embodiment. Additionally, it increases the separation between antenna feeds as an electromechanical relay is utilized which, despite component failure, can only connect one antenna signal to the receiver. The relay embodiment is much simpler, with much fewer circuit elements, and in some installations minimizes the number of coax cables which must be laid between the antenna and the home.
A few of the functional features and advantages of this improved polarity switch have been mentioned above. A more complete understanding of these features can be gained by reviewing the drawings and description of the preferred embodiment which follows.